1. Field of The Invention
This invention relates to an improvement of a turbocharger used in an internal combustion engine for automobiles and other uses.
2. Description of The Prior Art
In general, a turbocharger comprises a turbine rotor, a bearing housing which supports a shaft of the turbine rotor, a turbine housing which receives a turbine of the turbine rotor and is fixed to one end of the bearing housing and a compressor which is mounted on the other end of the bearing housing. The turbine, which is driven by the pressure of exhaust has from an engine, rotates a compressor, which compresses intake air and feeds it into a cylinder of the engine.
Usually, a turbocharger is lubricated and cooled by virtue of a lubricating oil of an engine. Therefore, no problem will occur in lubrication and cooling of a bearing housing during engine operation, since the lubricating oil is supplied to the bearing housing by the action of an oil pump of the engine.
However, when the engine is stopped, the oil pump will stop and supply no lubricating oil. This leads to a remarkable reduction of the cooling performance of the oil. Especially, after a high load operation, the turbine housing may have reached a very high temperature and therefore, without cooling by the lubricating oil, the bearing housing is heated by heat conduction from the turbine housing and sometimes takes a temperature higher than 300.degree. C. in several minutes after engine stoppage.
Such high temperature may carbonize the lubricating oil in the bearing housing and cause degradation of the oil. The oil carbonization may also deteriorate the bearing and reduce the performance of the turbocharger. In the worst cases, the turbocharger may be fractured.
Conventional preventive measures against these problems include prevention of sudden stop of an engine which has been operated at a high load and continuation of idling operation for a certain period in accordance with a previous engine load. However, these conventional measures are taken at an operator's will and therefore are not completely practiced.